Such a method and control unit are described, for example, in German Publication Patent Application No. 101 31 507, which describes an injection system for an internal combustion engine in which fuel is conveyed into a fuel accumulator by a metering unit and a high-pressure pump. The injection system also includes two closed-loop control circuits to regulate the pressure in the fuel accumulator. A first closed-loop control circuit regulates this pressure by suitable control of a pressure-control valve on the high-pressure side of the injection system. A second closed-loop control circuit regulates the pressure in the fuel accumulator by suitable triggering of the metering unit on the low-pressure side of the injection system. To keep inaccuracies in the high-pressure control of the pressure in the fuel accumulator as low as possible—such inaccuracies being attributable to manufacturing tolerances in the serial production of the pressure-control valve—a method is described for generating an individual characteristic curve that represents the actual response of a particular pressure-control valve. Rather than using an approximated or standardized characteristic curve, the pressure-control valve is then controlled according to this individual characteristic curve within the framework of the first closed-loop control circuit.
Inaccuracies may occur in the control of the pressure in the fuel accumulator via the second closed-loop control circuit as well. This is true especially when, for instance, the response of an actually used metering unit deviates from an expected response of a standardized metering unit because of manufacturing tolerances.